Refrigeration fluids, commonly known as refrigerants, are the media used for heat transfer in a refrigeration system to absorb heat when the fluid is at a low temperature and low pressure and to give up heat when the fluid is at a high temperature and a high pressure. This involves changes of state of the refrigerant. The common refrigerants for commercial refrigeration system include R-22, R-404a, R-507, R-410, R-407, R-134a, among others and are widely used. Natural gas (consisting of 95% methane, such as R-50) and propane (R-290) are also typical refrigerants along with others belonging to the propane and methane series. At present time, a natural refrigerant such as carbon dioxide (R-744) is becoming popular. On the other hand, all refrigerants are typically liquefied gases that, in the process of evaporation, produce refrigeration effects utilized for numerous applications.
Commercial refrigeration and HVAC systems typically use refrigerants to deliver cooling for a variety of applications. These applications include refrigerated cases, freezers, and air conditioning systems, as well as many other types of systems. These refrigeration systems are “closed loop systems.” A closed loop system is defined as a system that contains a defined amount of refrigerant that circulates through evaporation and condensing stages to alternately cool through the evaporation process and through off heat through the condensing process.
Closed loop refrigeration systems operate at optimum efficiency when they have a quantity of refrigerant that facilitates the refrigeration process. This quantity of refrigerant is typically referred to as a “full charge.” The design of the system, its size and components are factors that determine the appropriate full charge. For example, a typical supermarket may have as much as 3,000 to 5,000 pounds of refrigerant in its refrigeration and air conditioning systems. When a new system is built, it is important to determine and document the initial full charge of refrigerant required to enable the system to operate at its optimum designed level of efficiency. This is the “initial full charge.”
Once a closed loop system has received its initial full charge, the system typically experiences changes in the level of refrigerant. These changes in refrigerant level can be caused by a broad range of factors. Changes in temperature can change the density of the refrigerant which can require the addition or removal of refrigerant to maintain the optimum operation of the system. The servicing or replacement of components may require the controlled removal of refrigerant from the system to facilitate the component replacement. In addition, leaks can develop in the components of the system or in pipes connecting the components from a broad range of causes. Statistically, the average loss in these systems can approach thirty to forty percent each year.
Often, low levels of refrigerant are not easily identifiable. For example, in a supermarket, there may be complaints about a temperature problem, such as the ice cream in its refrigerated case getting soft. What may be occurring is what is generally called “starving the system”: there is not enough liquid refrigerant in the system. The source of the leak is investigated and repaired. Then it is necessary to recharge the system with an appropriate amount of refrigerant to achieve a full charge.
U.S. Pat. No. 5,097,667 to Gramkow demonstrates a typical method of recharging a refrigeration system. However, it does not measure the amount transferred.
Current regulations, namely section 608 of the Clean Air Act, require service practices that maximize the recycling of ozone depleting compounds (refrigerants) during the servicing and disposal of air conditioning and refrigeration equipment. The regulations allow the addition of refrigerant to a depleted refrigeration system, but the regulations set restrictions on the amount of refrigerant that may leak from the system.
Owners of equipment with charges of refrigerant greater than fifty pounds are required to repair leaks in the equipment when those leaks would result in the loss of more than a certain percentage of the refrigerant charge of the equipment over a continuous one year period. For the commercial and industrial process refrigeration sectors, including supermarkets, refrigerated warehouses, and other large refrigerated facilities, refrigerant leaks must be repaired such that the appliance would not exceed a calculated leak rate of 35% for a period of greater than 30 days per the guidelines of the Environmental Protection Agency (EPA) in the United States. For all other sectors, including comfort cooling, leaks must be repaired such that the calculated leak rate does not exceed 15% for a period greater than 30 days. The calculation for replacement rate is the projected leak rate over the next year based on the most current replacement rate rather than the total quantity of refrigerant lost, although this may be taken into consideration in the event of a government audit.
For instance, owners of a commercial refrigeration system containing one hundred pounds of charge must repair leaks if they find that the system has lost ten pounds of charge over the past month. Although ten pounds represents only ten percent of the system charge in this case, a leak rate of ten pounds per month would result in the release of over 100% of the charge over the year.
To track leak rates, owners of air conditioning and refrigeration equipment with more than fifty pounds of charge must keep records of the quantity of refrigerant added to their equipment during servicing and maintenance procedures, as well as the type of repair and method of leak testing. Owners are required to repair leaks within thirty days of discovery if the leaks would result in a calculated rate greater than the required limit. This requirement is waived if, within thirty days of discovery, the owner develops a one year retrofit or retirement plan for the leaking equipment. An owner of industrial process refrigeration equipment may qualify for additional time under certain circumstances and may have other unique requirements for leak repair verification.
In a typical commercial or industrial refrigeration system there may be 2,000 or more fittings connecting system components, and a leak can occur in any of them. Therefore, there is a great potential for leakage and enormous financial consequences.
The typical method technicians use to measure refrigerant today is to weigh their supply tank on a scale before and after transfer of refrigerant from the supply tank to the refrigeration systems. Another method known in the art is a system based upon a digital scale. U.S. Pat. No. 6,609,381 to Morgan demonstrates the digital scale method. The container is placed on a digital scale platform and the scale records the beginning weight and the ending weight. The amount used can be calculated manually or displayed on the scale's user interface.
These methods are inconvenient and prone to error and malfunction due to the mechanical strain on the scales, repeated use, or external influence which might bias the resulting calculation. In addition, in many cases, technicians may simply estimate the amount of refrigerant based on how heavy the container “feels”, which, if inaccurate, can impact the cost of the service call and/or bias the EPA rate calculation.